390 NEUROLOGY, OR ANATOMY OF NERVOUS SYSTEM 



The posterior wall of the tympanum presents above one 

 large and several small apertures leading to the mastoid cells. 



The anterior extremity opens into two canals separated by 

 a process of bone, the processus cockle arif or mis. The upper of 

 these canals is the smaller and transmits the tensor tympani; 

 the lower contains the Eustachian tube, and osteocartilaginous 

 passage Ij inches long, leading to the pharynx. Both of these 

 canals run in a direction downward, forward, and inward. 



The osseous part of the Eustachian tube is \ inch long, and 

 to its lower end is attached the triangular piece of fibrocartilage 

 forming the remainder of the tube. The edges of the cartilage 

 are not in contact, but are joined by fibrous tissue. The tube 

 is wide at its lower extremity, and opens at the upper and 

 lateral part of the pharynx, above the hard palate and behind 

 the lower turbinated bone. It is lined by epithelium continuous 

 with that of the pharynx. 



The ossicula are three small movable bones, named the 

 malleus, incus, and stapes. The first is attached to the mem- 

 brana tympani; the second is between the other two; the 

 last named is attached to the fenestra ovalis. 



The malleus (a hammer) consists of a head, neck, and three 

 processes, viz., the processus gracilis, the processus brevis, 

 and the manubrium. The head articulates with the incus. 

 The neck is below it, and rests on a prominence which is con- 

 nected with the three processes. The manubrium tapers to 

 its extremity, which is flattened, and it is connected with 

 the membrana tympani. The tensor tympani is attached to 

 its inner side near its upper end, and from its root springs 

 the processus brevis. The processus gracilis is long and slender, 

 and is connected by bone and fibrous tissue with the Glaserian 

 fissure. 



The incus (an anvil) has a body and two processes. The 

 body presents a saddle-shaped articular surface for the malleus; 

 the short process is conical, looks backward, and is attached to 

 the opening which leads to the mastoid cells; the long process 

 descends behind the manubrium of the malleus, to end in 

 the os orbiculare, or lenticular process, which articulates with 

 the head of the stapes. 



The stapes (a stirrup) presents a head, which articulates 

 with the os orbiculare; a neck, to which is attached the stapedius 

 muscle; and two crura, diverging from the neck, and connected 



